Lubricant composition

ABSTRACT

The present invention provides a lubricating oil composition comprising: a lubricating base oil; 1.0% by mass or more and 15.0% by mass or less of a dispersant poly(meth)acrylate compound having the weight average molecular weight of 20000 or more and 200000 or less; 0.05% by mass or more and 6.0% by mass or less of a thiadiazole compound; 1.5% by mass or more and 4.0% by mass or less of a polysulfide compound; and 0.2% by mass or more and 1.5% by mass or less of a friction modifier, based on the total amount of the lubricating oil composition, wherein the mass ratio of the polysulfide compound content to the thiadiazole compound content (polysulfide compound/thiadiazole compound) is 0.4 or more and 50 or less, and the kinematic viscosity at 100° C. of the lubricating oil composition is 7.0 mm 2 /s or more and 35.0 mm 2 /s or less.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition.

BACKGROUND ART

Lubricating oil compositions have been used for machines such asinternal combustion engines and speed change gears in order to make theoperation thereof smooth until now. In lubricating oil compositions,various additives such as antiwear agents, metal-based detergents,ash-free dispersants and antioxidants are mixed into lubricating baseoils according to performance requirements (refer to, for example,Patent Literature 1 to 3).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.2001-279287

Patent Literature 2: Japanese Unexamined Patent Publication No.2002-129182

Patent Literature 3: Japanese Unexamined Patent Publication No.H8-302378

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a lubricating oilcomposition that is excellent in all of load resistance, fatigue life,shear stability and friction characteristics.

Solution to Problem

The present invention provides a lubricating oil composition comprising:a lubricating base oil; 1.0% by mass or more and 15.0% by mass or lessof a dispersant poly(meth)acrylate compound having the weight averagemolecular weight of 20000 or more and 200000 or less; 0.05% by mass ormore and 6.0% by mass or less of a thiadiazole compound; 1.5% by mass ormore and 4.0% by mass or less of a polysulfide compound; and 0.2% bymass or more and 1.5% by mass or less of a friction modifier, based onthe total amount of the lubricating oil composition, wherein the massratio of the polysulfide compound content to the thiadiazole compoundcontent (polysulfide compound/thiadiazole compound) is 0.4 or more and50 or less, and the kinematic viscosity at 100° C. of the lubricatingoil composition is 7.0 mm²/s or more and 35.0 mm²/s or less.

It is preferable that the friction modifier contains at least oneselected from the group consisting of primary or secondary amidefriction modifiers and primary or secondary amine friction modifiers.

The lubricating oil composition is preferably used as a lubricating oilcomposition for gear oils.

The lubricating oil composition is preferably used as a lubricating oilcomposition for final reduction gear oils.

Advantageous Effects of Invention

According to the present invention, a lubricating oil composition thatis excellent in all of load resistance, fatigue life, shear stabilityand friction characteristics can be provided.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detailhereinafter.

A lubricating oil composition according to this embodiment contains (A)a lubricating base oil, (B) a dispersant poly(meth)acrylate compound,(C) a thiadiazole compound, (D) a polysulfide compound and (E) afriction modifier.

The (A) lubricating base oil (hereinafter called also an “(A)ingredient”) may be a known base oil used for lubricating oils, and maybe, for example, a mineral oil base oil, a synthetic base oil or amixture of both.

The mineral oil base oil includes mineral oil base oils such asparaffinic and naphthenic base oils, normal paraffins and isoparaffinsobtained by refining a lubricating oil fraction obtained by atmosphericdistillation and vacuum distillation of crude oil through one orsuitably combined two or more of refining treatments such as solventdeasphalting, solvent extraction, hydrocracking, solvent dewaxing,contact dewaxing, hydrorefining, sulfuric acid treatment and claytreatment. One of these mineral oil base oils may be used alone, and twoor more thereof may be used in combination at any rate.

Preferable mineral oil base oils include the following base oils:

(1) a distilled oil obtained by the atmospheric distillation of aparaffinic crude oil and/or a mixed-base crude oil;(2) a whole vacuum gas oil (WVGO) of an atmospheric distillationresidual oil of a paraffinic crude oil and/or a mixed-base crude oil;(3) wax obtained by a process of dewaxing a lubricating oil and/orFischer Tropsch wax produced by a GTL process and the like;(4) a mild hydrocracking treatment oil (MHC) of one or a blended oil oftwo or more selected from the above (1) to (3);(5) a blended oil of two or more oils selected from the above (1) to(4);(6) a deasphalted oil (DAO) of the above (1), (2), (3), (4), or (5);(7) a mild hydrocracking treatment oil (MHC) of the above (6); and(8) a lubricating oil obtained by using a blended oil of two or moreoils selected from the above (1) to (7) or the like as a raw materialoil, refining this raw material oil and/or a lubricating oil fractioncollected therefrom in a usual refining method and collecting alubricating oil fraction.

Here, the usual refining method is not limited particularly, and may beany refining method used at the time of production of base oils.Examples of the usual refining method include the following refiningmethods:

(a) hydrorefining such as hydrocracking or hydrofinishing;(b) solvent refining such as furfural solvent extraction;(c) dewaxing such as solvent dewaxing or contact dewaxing;(d) clay refining by acid clay, activated clay or the like;(e) chemical (acid or alkali) refining such as sulfuric acid treatmentor sodium hydroxide treatment.One of these refining methods may be adopted alone, and two or morethereof may be adopted in any combination and any order.

The synthetic base oils include poly-α-olefins or hydrides thereof;isobutene oligomers or hydrides thereof; isoparaffins; alkylbenzenes;alkylnaphthalenes; diesters (such as ditridecyl glutarate,di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, di-isodecyl adipate,ditridecyl adipate, and di-2-ethylhexyl sebacate); polyol esters (suchas trimethylolpropane caprylate, trimethylolpropane pelargonate,pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate);polyoxyalkylene glycols; dialkyldiphenyl ethers; and polyphenyl ether,and poly-α-olefins are preferable particularly. Examples of thepoly-α-olefins include oligomers or co-oligomers of α-olefins (such as1-octene oligomers, decene oligomers, and ethylene-propyleneco-oligomers) having 2 or more and 32 or less carbon atoms, andpreferably 6 or more and 16 or less, and hydrides thereof. One of thesesynthetic base oils may be used alone, and two or more thereof may beused in combination at any rate.

The kinematic viscosity at 40° C. of a lubricating base oil ispreferably 20 mm²/s or more, more preferably 50 mm²/s or more, and stillmore preferably 90 mm²/s or more. When the kinematic viscosity at 40° C.of a lubricating base oil is 20 mm²/s or more, oil film formationbecomes satisfactory, and it becomes easier to obtain a lubricating oilcomposition that is excellent in lubricity and the evaporation loss ofwhich under a high temperature condition is lower. The kinematicviscosity at 40° C. of a lubricating base oil is preferably 180 mm²/s orless, more preferably 140 mm²/s or less, and still more preferably 130mm²/s or less. When the kinematic viscosity at 40° C. of a lubricatingbase oil is 180 mm²/s or less, the fluid resistance becomes lower, andtherefore, it becomes easier to obtain a lubricating oil composition therotational resistance of which is lower.

The kinematic viscosity at 100° C. of a lubricating base oil ispreferably 3.0 mm²/s or more, more preferably 5.0 mm²/s or more, andstill more preferably 10.0 mm²/s or more. When the kinematic viscosityat 100° C. of a lubricating base oil is 3.0 mm²/s or more, oil filmformation becomes satisfactory, and it becomes easier to obtain alubricating oil composition that is excellent in lubricity and theevaporation loss of which under a high temperature condition is lower.The kinematic viscosity at 100° C. of a lubricating base oil ispreferably 25 mm²/s or less, more preferably 18 mm²/s or less, and stillmore preferably 15 mm²/s or less. When the kinematic viscosity at 100°C. of a lubricating base oil is 25 mm²/s or less, the fluid resistancebecomes lower, and therefore, it becomes easier to obtain a lubricatingoil composition the rotational resistance of which is lower.

The viscosity index of a lubricating base oil is preferably 60 or more,more preferably 80 or more, and still more preferably 90 or more. Whenthe viscosity index is 60 or more, it becomes easier to obtain alubricating oil composition exhibiting better viscosity characteristicsin the range from low temperatures to high temperatures.

The kinematic viscosity and the viscosity index in the present inventionmean a kinematic viscosity and a viscosity index measured in accordancewith JIS K2283: 2000, respectively.

The sulfur content in a lubricating base oil may be 5000 ppm by mass orless, 4500 ppm by mass or less, or 4000 ppm by mass or less on the basisof the total amount of the lubricating base oil. The sulfur content in alubricating base oil can be measured by an ICP elementary analysismethod.

The content of the (A) ingredient may be, for example, 70% by mass ormore, 80% by mass or more, or 85% by mass or more on the basis of thetotal amount of the lubricating oil composition. The content of the (A)ingredient may be, for example, 95% by mass or less, 93% by mass orless, or 90% by mass or less on the basis of the total amount of thelubricating oil composition.

The (B) dispersant poly(meth)acrylate compound (hereinafter called alsoa “(B) ingredient”) contains a poly(meth)acrylate compound having adispersant group. The dispersant group is preferably anitrogen-containing dispersant group, and more preferably adimethylamino group.

The (B) ingredient preferably contains a poly(meth)acrylate compoundhaving at least one structural unit selected from a structural unitrepresented by the following formula (1) and a structural unitrepresented by the following formula (2).

[In the formula (1), R¹ represents a hydrogen atom or a methyl group, R²represents an alkylene group the carbon number of which is 1 to 18, E¹represents an amine residue or a heterocyclic residue having 1 to 2nitrogen atoms and 0 to 2 oxygen atoms, and in represents 0 or 1.]

[In the formula (2), R³ represents a hydrogen atom or a hydrocarbongroup, and E² represents an amine residue or a heterocyclic residuehaving 1 to 2 nitrogen atoms and 0 to 2 oxygen atoms.]

Examples of the alkylene group the carbon number of which is 1 to 18 andthat is represented by R² include an ethylene group, a propylene group,a butylene group, a pentylene group, a hexylene group, a heptylenegroup, an octylene group, a nonylene group, a decylene group, anundecylene group, a dodecylene group, a tridecylene group, atetradecylene group, a pentadecylene group, a hexadecylene group, aheptadecylene group, and an octadecylene group. These alkylene groupsmay be linear or branched.

The hydrocarbon group represented by R³ may be, for example, a linear orbranched hydrocarbon group the carbon number of which is 1 to 12.

Examples of the groups represented by E¹ and E² each include adimethylamino group, a diethylamino group, a dipropylamino group, adibutylamino group, an anilino group, a toluidino group, a xylidinogroup, an acetylamino group, a benzoylamino group, a morpholino group, apyrrolyl group, a pyrrolino group, a pyridyl group, a methylpyridylgroup, a pyrrolidinyl group, a piperidinyl group, a quinonyl group, apyrrolidonyl group, a pyrrolidono group, an imidazolino group, and apyrazino group.

The weight average molecular weight of a dispersant poly(meth)acrylateis preferably 20000 or more, more preferably 30000 or more, and stillmore preferably 40000 or more in view of an excellent fatigue life. Theweight average molecular weight of a dispersant poly(meth)acrylate ispreferably 200000 or less, more preferably 170000 or less, still morepreferably 110000 or less, and particularly preferably 50000 or less inview of excellent shear stability. The weight average molecular weightof a dispersant poly(meth)acrylate is 20000 or more and 200000 or less;preferably 20000 or more and 170000 or less; 20000 or more and 110000 orless; 20000 or more and 50000 or less; 30000 or more and 200000 or less;30000 or more and 170000 or less; 30000 or more and 110000 or less;30000 or more and 50000 or less; 40000 or more and 200000 or less; 40000or more and 170000 or less; 40000 or more and 110000 or less; or 40000or more and 50000 or less in view of compatibility between fatigue lifeand shear stability. The weight average molecular weight in the presentinvention means a weight average molecular weight measured by GPCanalysis (a value in terms of polystyrene (standard sample)).

The content of the (B) ingredient is preferably 1.0% by mass or more,more preferably 2.0% by mass or more, and still more preferably 2.5% bymass or more on the basis of the total amount of the lubricating oilcomposition in view of an excellent fatigue life. The content of the (B)ingredient is preferably 15.0% by mass or less, more preferably 9.0% bymass or less, and preferably 5.0% by mass or less on the basis of thetotal amount of the lubricating oil composition in view of excellentshear stability. The content of the (B) ingredient is 1.0% by mass ormore and 15.0% by mass or less, and preferably 1.0% by mass or more and9.0% by mass or less; 1.0% by mass or more and 5.0% by mass or less;2.0% by mass or more and 15.0% by mass or less; 2.0% by mass or more and9.0% by mass or less; 2.0% by mass or more and 5.0% by mass or less;2.5% by mass or more and 15.0% by mass or less; 2.5% by mass or more and9.0% by mass or less; or 2.5% by mass or more and 5.0% by mass or lesson the basis of the total amount of the lubricating oil composition inview of compatibility between fatigue life and shear stability.

The (C) thiadiazole compound (hereinafter called also a “(C)ingredient”) may be a known thiadiazole compound, and may be, forexample, a 1,3,4-thiadiazole compound represented by the followingformula (3), a 1,2,4-thiadiazole compound represented by the followingformula (4), or a 1,2,3-thiadiazole compound represented by thefollowing formula (5).

where R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ each independently represent a hydrogenatom or a hydrocarbon group the carbon number of which is 1 to 20, anda, b, c, d, e and f each independently represent an integer of 0 to 8.

Specific examples of such a thiadiazole compound include2,5-bis(n-hexyldithio)-1,3,4-thiadiazole;2,5-bis(n-octyldithio)-1,3,4-thiadiazole;2,5-bis(n-nonyldithio)-1,3,4-thiadiazole;2,5-bis(1,1,3,3-tetramethylbutyldithio)-1,3,4-thiadiazole;3,5-bis(n-hexyldithio)-1,2,4-thiadiazole;3,5-bis(n-octyldithio)-1,2,4-thiadiazole;3,5-bis(n-nonyldithio)-1,2,4-thiadiazole;3,5-bis(1,1,3,3-tetramethylbutyldithio)-1,2,4-thiadiazole;4,5-bis(n-hexyldithio)-1,2,3-thiadiazole;4,5-bis(n-octyldithio)-1,2,3-thiadiazole;4,5-bis(n-nonyldithio)-1,2,3-thiadiazole; and4,5-bis(1,1,3,3-tetramethylbutyldithio)-1,2,3-thiadiazole.

The content of the (C) ingredient is preferably 0.05% by mass or more,more preferably 0.2% by mass or more, still more preferably 1.0% by massor more, and particularly preferably 1.5% by mass or more on the basisof the total amount of the lubricating oil composition in view ofexcellent load resistance. The content of the (C) ingredient ispreferably 6.0% by mass or less, more preferably 4.5% by mass or less,and still more preferably 3.0% by mass or less on the basis of the totalamount of the lubricating oil composition in view of an excellentfatigue life. The content of the (C) ingredient is 0.05% by mass or moreand 6.0% by mass or less; preferably 0.05% by mass or more and 4.5% bymass or less; 0.05% by mass or more and 3.0% by mass or less; 0.2% bymass or more and 6.0% by mass or less; 0.2% by mass or more and 4.5% bymass or less; 0.2% by mass or more and 3.0% by mass or less; 1.0% bymass or more and 6.0% by mass or less; 1.0% by mass or more and 4.5% bymass or less; 1.0% by mass or more and 3.0% by mass or less; 1.5% bymass or more and 6.0% by mass or less; 1.5% by mass or more and 4.5% bymass or less; or 1.5% by mass or more and 3.0% by mass or less on thebasis of the total amount of the lubricating oil composition in view ofcompatibility between load resistance and fatigue life.

The (D) polysulfide compound (hereinafter called also a “(D)ingredient”) may be a known polysulfide compound, and may be, forexample, a compound represented by the following formula (6).

R¹⁰—S_(x)—R¹¹  (6)

In the formula (6), R¹⁰ and R¹¹ each independently represents a linearor branched alkyl group the carbon number of which is 3 to 20, an arylgroup the carbon number of which is 6 to 20, an alkaryl group the carbonnumber of which is 6 to 20, or an aralkyl group the carbon number whichis 6 to 20, and x represents an integer of 2 to 6, and preferably aninteger of 2 to 5.

The content of the (D) ingredient is preferably 1.5% by mass or more,more preferably 1.8% by mass or more, and still more preferably 2.0% bymass or more on the basis of the total amount of the lubricating oilcomposition in view of excellent extreme pressure characteristics. Thecontent of the (D) ingredient is preferably 4.0% by mass or less, morepreferably 3.0% by mass or less, still more preferably 2.5% by mass orless, and particularly preferably 2.2% by mass or less on the basis ofthe total amount of the lubricating oil composition in view of anexcellent fatigue life. The content of a (D) ingredient is 1.5% by massor more and 4.0% by mass or less; preferably 1.5% by mass or more and3.0% by mass or less; 1.5% by mass or more and 2.5% by mass or less;1.8% by mass or more and 4.0% by mass or less; 1.8% by mass or more and2.5% by mass or less; 1.8% by mass or more and 2.2% by mass or less;2.0% by mass or more and 4.0% by mass or less; 2.0% by mass or more and2.5% by mass or less; or 2.0% by mass or more and 2.2% by mass or lesson the basis of the total amount of the lubricating oil composition inview of compatibility between extreme pressure characteristics andfatigue life.

The (E) friction modifier (hereinafter called also an “(E) ingredient”)may be a known friction modifier, and may be, for example, an amine,amide, imide, fatty acid ester, fatty acid, aliphatic alcohol, oraliphatic ether friction modifier. The (E) ingredient preferablycontains at least one friction modifier selected from the groupconsisting of primary or secondary amine friction modifiers and primaryor secondary amide friction modifiers.

Examples of the primary or secondary amine friction modifier includealkylamines such as methylamine, ethylamine, propylamine, butylamine,pentylamine, hexylamine, heptylamine, octylamine, nonylamine,decylamine, undecylamine, dodecylamine (laurylamine), tridecylamine,tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine,octadecylamine (stearylamine), docosylamine (behenylamine),dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine,dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine,diundecylamine, didodecylamine, ditridecyl amine, ditetradecylamine,dipentadecylamine, dihexadecylamine, diheptadecylamine,dioctadecylamine, methylethyl amine, methylpropylamine, methylbutylamine, ethylpropylamine, ethylbutylamine, and propylbutylamine that havealkyl groups with 1 to 30 carbon atoms (these alkyl groups may be linearor branched); alkenylamines such as ethenylamine, propenylamine,butenylamine, octenylamine, and oleylamine that have alkenyl groups with2 to 30 carbon atoms (these alkenyl groups may be linear or branched);alicyclic amines such as cyclohexylamine; and alkylenediamines such asmethylenediamine, ethylenediamine, propylenediamine, and butylenediaminethat have alkylene groups with 1 to 30 carbon atoms. Among these,alkylamines and alkenyl amines are preferable. The numbers of carbonatoms of the alkyl groups of alkylamines are preferably 4 to 28, andmore preferably 6 to 25. The numbers of carbon atoms of the alkenylgroup of alkenyl amines are preferably 4 to 28, and more preferably 6 to25.

Examples of the primary or secondary amide friction modifier includesaturated fatty acid amides such as ethanoic acid amide, propanoic acidamide, butanoic acid amide, octanoic acid amide, decanoic acid amide,dodecanoic acid amide, hexadecanoic acid amide, octadecanoic acid amide,docosanoic acid amide that have alkyl groups with 1 to 30 carbon atoms(these alkyl groups may be linear or branched); unsaturated fatty acidamides such as oleic acid amide and erucic acid amide that have alkenylgroups with 2 to 30 carbon atoms (these alkenyl groups may be linear orbranched). The numbers of carbon atoms of the alkyl groups of saturatedfatty acid amides are preferably 4 to 28, and more preferably 6 to 25.The numbers of carbon atoms of the alkenyl groups of unsaturated fattyacid amides are preferably 4 to 28, more preferably 6 to 25.

The content of the (E) ingredient is preferably 0.2% by mass or more,more preferably 0.5% by mass or more, and still more preferably 0.7% bymass or more on the basis of the total amount of the lubricating oilcomposition in view of excellent friction characteristics. The contentof the (E) ingredient is preferably 1.5% by mass or less, morepreferably 1.2% by mass or less, and still more preferably 0.9% by massor less on the basis of the total amount of the lubricating oilcomposition in view of excellent oxidation stability. The content of the(E) ingredient is 0.2% by mass or more and 1.5% by mass or less; andpreferably 0.2% by mass or more and 1.2% by mass or less; 0.2% by massor more and 0.9% by mass or less; 0.5% by mass or more and 1.5% by massor less; 0.5% by mass or more and 1.2% by mass or less; 0.5% by mass ormore and 0.9% by mass or less; 0.7% by mass or more and 1.5% by mass orless; 0.7% by mass or more and 1.2% by mass or less; or 0.7% by mass ormore and 0.9% by mass or less on the basis of the total amount of thelubricating oil composition in view of compatibility between frictioncharacteristics and oxidation stability.

In the lubricating oil composition, the mass ratio of the content of the(D) polysulfide compound to the content of the (C) thiadiazole compound((D) polysulfide compound/(C) thiadiazole compound) is 0.4 or more and50 or less, more preferably 0.5 or more and 30 or less, still morepreferably 1.0 or more and 15 or less, and particularly preferably 1.0or more and 10 or less in view of an excellent fatigue life. The massratio ((D) ingredient/(C) ingredient) may be 0.4 or more, 0.5 or more,and 1.0 or more, and may be 50 or less, 30 or less, 15 or less, and 10or less.

In addition to the above (A) to (E) ingredients, the lubricating oilcomposition may further contain other additives if needed. Examples ofthe other additives include an extreme pressure agent, a viscositymodifier, a metal-based detergent, an ash-free dispersant, anantioxidant, a corrosion inhibitor, an antirust, a demulsifier, a metaldeactivator, and a defoaming agent.

The extreme pressure agent includes phosphorus-based extreme pressureagents such as phosphites and phosphates as well as amine salts, metalsalts and derivatives thereof; and sulfur-based extreme pressure agentssuch as dithiocarbamate, zinc dithiocarbamate, molybdenumdithiocarbamate (MoDTC), olefin sulfide, and sulfurized oil and fat.

Examples of the viscosity modifier include non-dispersant poly(meth)acrylate viscosity modifiers; styrene-maleic anhydride estercopolymer viscosity modifiers; non-dispersant or dispersantethylene-α-olefin copolymers or hydrides thereof; polyisobutylene or thehydride thereof; styrene-diene hydrogenated copolymers; andpolyalkylstyrenes.

The metal-based detergent includes salicylate detergents, phenatedetergents, sulfonate detergents. These metal-based detergents may beany of a normal salt, a basic salt and a perbasic salt with an alkalimetal or an alkaline earth metal.

The ash-free dispersant includes nitrogen-containing compounds such assuccinimide, benzylamine, polyamines, and Mannich bases that havealkenyl groups or alkyl groups derived from polyolefins; andboron-modified nitrogen-containing compounds (boron-based ash-freedispersants) such as boron-modified succinimide obtained by modifyingthese nitrogen-containing compounds with boron compounds such as boricacid and borates.

The antioxidant includes ash-free antioxidants such as phenol and amineantioxidants; and metal-based antioxidants such as copper-based andmolybdenum-based antioxidants. Specific examples of the phenol ash-freeantioxidants include 4,4′-methylene-bis-(2,6-di-tert-butylphenol),4,4′-bis(2,6-di-tert-butylphenol), and specific examples of amineash-free antioxidants include phenyl-α-naphthylamine,alkylphenyl-α-naphthylamines, dialkyldiphenylamines, and diphenylamine.

Examples of the corrosion inhibitor include benzotriazole, tolyltriazoleand imidazole compounds.

Examples of the antirust include alkenyl succinates, polyhydric alcoholesters, petroleum sulfonates, alkylbenzene sulfonates, anddinonylnaphthalene sulfonate.

Examples of the demulsifier include polyalkylene glycol-based non-ionicsurfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene alkyl naphthyl ethers.

Examples of the metal deactivator include imidazoline, pyrimidinederivatives, and benzotriazol or derivatives thereof.

Examples of the defoaming agent include silicone oil, alkenyl succinicacid derivatives, the esters of polyhydroxy aliphatic alcohols andlong-chain fatty acids, and the ester of methyl salicylate ando-hydroxybenzyl alcohol the kinematic viscosity of which at 25° C. is1000 mm²/s or more and 100000 mm²/s or less.

The content of the other additives may be 0.01 to 20% by mass on thebasis of the total amount of the lubricating oil composition.

The kinematic viscosity at 40° C. of the lubricating oil composition ispreferably 70 mm²/s or more, more preferably 100 mm²/s more, and stillmore preferably 120 mm²/s or more. Since the kinematic viscosity at 40°C. is 60 mm²/s or more, the lubricating oil composition tends to beexcellent in oil film retentivity and evaporativity on lubricatedportions. The kinematic viscosity at 40° C. of the lubricating oilcomposition is preferably 250 mm²/s or less, more preferably 230 mm²/sor less, and still more preferably 210 mm²/s or less. Since thekinematic viscosity at 40° C. is 260 mm²/s or less, the lubricating oilcomposition tends to be excellent in cold flow property and fuelefficiency.

The kinematic viscosity at 100° C. of the lubricating oil composition ispreferably 7.0 mm²/s or more, more preferably 10.0 mm²/s or more, andstill more preferably 13.0 mm²/s or more. Since the kinematic viscosityat 100° C. is 7.0 mm²/s or more, the lubricating oil composition isexcellent in load resistance and fatigue life. The kinematic viscosityat 100° C. of the lubricating oil composition is preferably 35.0 mm²/sor less, more preferably 25.0 mm²/s or less, and still more preferably20.0 mm²/s or less. Since the kinematic viscosity at 100° C. is 35.0mm²/s or less, the lubricating oil composition tends to be excellent incold flow property and fuel efficiency. In view of excellence in all ofload resistance, fatigue life, cold flow property and fuel efficiency,the kinematic viscosity at 100° C. of the lubricating oil composition is7.0 mm²/s or more and 35.0 mm²/s or less; preferably 7.0 mm²/s or moreand 25.0 mm²/s or less; 7.0 mm²/s or more and 20.0 mm²/s or less; 10.0mm²/s or more and 35.0 mm²/s or less; 10.0 mm²/s or more and 25.0 mm²/sor less; 10.0 mm²/s or more and 20.0 mm²/s or less; 13.0 mm²/s or moreand 35.0 mm²/s or less; 13.0 mm²/s or more and 25.0 mm²/s or less; or13.0 mm²/s or more and 20.0 mm²/s or less.

The content of a sulfur element (C_(S)) in a lubricating oil compositionmay be, for example, 10000 ppm by mass or more, and may be 31000 ppm bymass or less on the basis of the total amount of the lubricating oilcomposition. A sulfur element in a lubricating oil composition isderived from a sulfur element contained in the lubricating base oil andthe additives such as the (C) and (D) ingredients.

The content of a phosphorus element (C_(P)) in the lubricating oilcomposition may be, for example, 700 ppm by mass or more, and may be2000 ppm by mass or less on the basis of the total amount of alubricating oil composition. A phosphorus element in a lubricating oilcomposition is derived from a phosphorus element contained in additivessuch as a phosphorus-based extreme pressure agent.

The content of a boron element (C_(B)) in the lubricating oilcomposition may be, for example, 30 ppm by mass or more, and may be 200ppm by mass or less on the basis of the total amount of a lubricatingoil composition. A boron element in a lubricating oil composition isderived from a boron element contained in additives such as aboron-based ash-free dispersant.

In a lubricating oil composition, the respective contents of a sulfurelement, a phosphorus element and a boron element (ppm by mass; on thebasis the total amount of the lubricating oil composition) preferablysatisfy the following expression (7) in view of more excellent loadresistance and a more excellent fatigue life.

0.05≤C_(S)/(C_(P)×C_(B))≤0.50  (7)

C_(S)/(C_(P)×C_(B)) is preferably 0.05 or more, more preferably 0.07 ormore, still more preferably 0.12 or more, and particularly preferably0.25 or more in view of more excellent load resistance.C_(S)/(C_(P)×C_(B)) is preferably 0.50 or less, more preferably 0.45 orless, still more preferably 0.40 or less, and particularly preferably0.35 or less in view of a more excellent fatigue life. The respectivecontents of a sulfur element, a phosphorus element and a boron elementcan be measured by an ICP elementary analysis method.

A lubricating oil composition according to this embodiment can be usedfor a usual use of lubricating oils and preferably used as a lubricatingoil composition for gear oils. More specifically, the lubricating oilcomposition is preferably applied to manual transmissions for cars,automatic transmissions, continuously variable transmission or finalreduction gears, or industrial gear systems. The lubricating oilcomposition is particularly preferably used as a lubricating oilcomposition for final reduction gear oils.

EXAMPLES

Although the present invention will be described more specificallyhereinafter on the basis of Examples, the present invention is notlimited to the following Examples.

Lubricating oil compositions were prepared by using lubricating baseoils and additives shown below. The composition of the lubricating oilcompositions is shown in Tables 1 to 5.

[Lubricating Base Oil]

A-1: a solvent-refined mineral oil (Gr I, kinematic viscosity at 40° C.:22.7 mm²/s, kinematic viscosity at 100° C.: 4.4 mm²/s, viscosity index:102, sulfur content: 0.14% by mass)A-2: a solvent-refined mineral oil (Gr I, kinematic viscosity at 40° C.:478.3 mm²/s, kinematic viscosity at 100° C.: 31.6 mm²/s, viscosityindex: 97, sulfur content: 0.48% by mass)A-3: a solvent-refined mineral oil (Gr I, kinematic viscosity at 40° C.:95.1 mm²/s, kinematic viscosity at 100° C.: 10.9 mm²/s, viscosity index:98, sulfur content: 0.58% by mass)A-4: a hydrorefined mineral oil (Gr III, kinematic viscosity at 40° C.:46.71 mm²/s, kinematic viscosity at 100° C.: 7.595 mm²/s, viscosityindex: 129, sulfur content: <10 ppm by mass)A-5: a hydrorefined mineral oil (Gr III, kinematic viscosity at 40° C.:8.73 mm²/s, kinematic viscosity at 100° C.: 2.435 mm²/s, viscosityindex: 98, sulfur content: <10 ppm by mass)A-6: a poly-α-olefin (Gr IV, kinematic viscosity at 40° C.: 405 mm²/s,kinematic viscosity at 100° C.: 50 mm²/s, viscosity index: 187, sulfurcontent: <10 ppm by mass)

[Additives]

B-1: a dispersant poly(meth)acrylate (weight average molecular weight:40000)B-2: a dispersant poly(meth)acrylate (weight average molecular weight:60000)B-3: a dispersant poly(meth)acrylate (weight average molecular weight:150000)b-1: a dispersant poly(meth)acrylate (weight average molecular weight:10000)b-2: a dispersant poly(meth)acrylate (weight average molecular weight:250000)b-3: a non-dispersant poly(meth)acrylate (weight average molecularweight: 40000)b-4: a non-dispersant poly(meth)acrylate (weight average molecularweight: 150000)C-1: 2,5-bis(alkyldithio)-1,3,4-thiadiazole (sulfur element content:36.0% by mass)C-2: 2,5-bis(alkyldithio)-1,3,4-thiadiazole (sulfur element content:34.7% by mass)D-1: polysulfide (sulfur element content: 45.8% by mass)E-1: oleylamineE-2: 2-ethylhexylamineE-3: distearylamineE-4: oleic acid amideF-1: di-n-butyl phosphite (phosphorus element content: 15.5% by mass)G-1: 10% by mass of a boron-based dispersant, 0.1% by mass of an amineantioxidant, 15% by mass of a phosphoric ester, 0.5% by mass of adefoaming agent, and an additive package containing 10% by mass of adiluent oilG-2: 15% by mass of a boron-based dispersant, 0.1% by mass of an amineantioxidant, 17% by mass of a phosphoric ester, 0.5% by mass of adefoaming agent, and an additive package containing 10% by mass of adiluent oilG-3: 0.1% by a mass of boron-based dispersant, 0.1% by mass of an amineantioxidant, 10% by mass of a phosphoric ester, 0.5% by mass of adefoaming agent, and an additive package containing 5% by mass of adiluent oil

For the lubricating oil compositions, evaluation tests shown below wereconducted. Results are illustrated in Tables 1 to 5.

[Load Resistance Test]

For the lubricating oil compositions, weld loads (WL) at 1800 rpm weremeasured by using a high-speed four ball tester on the basis of ASTMD2596. A heavier weld load (for example, 3089 N or more) means a higherload resistance in the test.

[Fatigue Life Test]

The fatigue life of gears until pitching occurs under the followingconditions was evaluated by using a unisteel rolling fatigue testingmachine. A longer fatigue life of the gears (for example, 1000 minutesor more) means a longer fatigue life of the lubricating oil composition.

Specimen: thrust needle

Contact pressure: 2 GPa

Oil temperature: 120° C.

Number of revolutions: 1410 rpm

[Shear Stability Test]

A sonic test was conducted under the following conditions on the basisof JPI-5S-29-88, the kinematic viscosity at 100° C. before and after thesonic test was measured, and a decrease in the viscosity was calculatedtherefrom. A smaller decrease in viscosity (for example, 8% or less)means a higher shear stability in the test.

Frequency: 10 kHz

Amplitude: 28 μM

Exposure time: 1 hour

[Coefficient of Friction Test]

The coefficients of friction between metals were evaluated under thefollowing conditions by using an LFW-1 testing machine. A smallercoefficient of friction between metals (for example, 0.15 or less) meansa better friction characteristic.

Specimen: block H60, ring S10

Load: 3113 N

Sliding velocity: 0.5 m/s

Oil temperature: 90° C.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Base oil composition (%by mass on the basis of the total amount of base oil) A-1 (38)   (38)  (38)   (38)   A-2 (62)   (62)   (62)   (62)   Base oil kinematicviscosity (mm²/s)  40° C. 118.1  118.1  118.1  118.1  100° C. 12.7 12.7  12.7  12.7  Sulfur content in base oil 3508    3508    3508   3508    (ppm by mass) Lubricating oil composition (% by mass on thebasis of the total amount of lubricating oil) Base oil Balance BalanceBalance Balance B-1 3.0 — — 1.0 B-2 — 3.0 — — B-3 — 3.0 — C-1 1.5 1.51.5 1.5 C-2 — — — — D-1 2.0 2.0 2.0 2.0 E-1  0.80  0.80  0.80  0.80 G-15.0 5.0 5.0 5.0 D ingredient content/C ingredient 1.4 1.4 1.4 1.4content Sulfur content in additives 14524     14524     14524    14524     (ppm by mass) Properties of lubricating oil Kinematicviscosity (mm²/s)  40° C. 144.3  148.5  167.3  127.7  100° C. 15.6 15.9  17.7  14.2  Viscosity index 111    111    116    110    Elementaryanalysis (ppm by mass) P 1100    1100    1100    1100    S 18032    18032     18032     18032     B 55   55   55   55   Evaluation testresults Load resistance (N) 3923    3923    3923    3923    Fatigue life(min) 1578    1590    1628    1228    Shear stability Kinematicviscosity after shear 15.5  15.7  17.0  14.1  Decrease in viscosity (%)0.7 1.6 4.2 0.6 Friction characteristics  0.09  0.09  0.09  0.09 Example5 Example 6 Example 7 Example 8 Base oil composition (% by mass on thebasis of the total amount of base oil) A-1 (38)   (38)   (38)   (38)  A-2 (62)   (62)   (62)   (62)   Base oil kinematic viscosity (mm²/s) 40° C. 118.1  118.1  118.1  118.1  100° C. 12.7  12.7  12.7  12.7 Sulfur content in base oil 3508    3508    3508    3508    (ppm by mass)Lubricating oil composition (% by mass on the basis of the total amountof lubricating oil) Base oil Balance Balance Balance Balance B-1 13.03.0 3.0 3.0 B-2 — — — — B-3 — — — — C-1 1.5 2.4 — 1.5 C-2 — — 1.5 — D-12.0 2.0 2.0 2.0 E-1  0.80  0.80  0.80  0.30 G-1 5.0 5.0 5.0 5.0 Dingredient content/C ingredient 1.4 0.8 1.4 1.4 content Sulfur contentin additives 14524     17944     14331     14524     (ppm by mass)Properties of lubricating oil Kinematic viscosity (mm²/s)  40° C. 201.4 144.3  144.3  144.3  100° C. 20.0  15.6  15.6  15.6  Viscosity index115    111    111    111    Elementary analysis (ppm by mass) P 1100   1100    1100    1100    S 18032     25052     17839     18032     B 55  55   55   55   Evaluation test results Load resistance (N) 3923   4903    3923    3923    Fatigue life (min) 2198    1432    1498   16852     Shear stability Kinematic viscosity after shear 19.4  15.5 15.5  15.5  Decrease in viscosity (%) 3.1 0.7 0.7 0.7 Frictioncharacteristics  0.09  0.09  0.09  0.12

TABLE 2 Example 9 Example 10 Example 11 Example 12 Base oil composition(% by mass on the basis of the total amount of base oil) A-1 (38)  (38)   (38)   (38)   A-2 (62)   (62)   (62)   (62)   Base oil kinematicviscosity (mm²/s)  40° C. 118.1  118.1  118.1  118.1  100° C. 12.7 12.7  12.7  12.7  Sulfur content in base oil 3508    3508    3508   3508    (ppm by mass) Lubricating oil composition (% by mass on thebasis of the total amount of lubricating oil) Base oil Balance BalanceBalance Balance B-1 3.0 3.0 3.0 3.0 C-1 1.5 1.5 1.5 1.5 D-1 2.0 2.0 2.02.0 E-1  1.00 — — — E-2 —  0.80 — — E-3 — —  0.80 — E-4 — — —  0.08 F-1— — — — G-1 5.0 5.0 5.0 5.0 G-2 — — — — G-3 — — — — D ingredientcontent/C ingredient 1.4 1.4 1.4 1.4 content Sulfur content in additives14524     14524     14524     14524     (ppm by mass) Properties oflubricating oil Kinematic viscosity (mm²/s)  40° C. 144.3  144.3  144.3 144.3  100° C. 15.6  15.6  15.6  15.6  Viscosity index 111    111   111    111    Elementary analysis (ppm by mass) P 1100    1100   1100    1100    S 18032     18032     18032     18032     B 55   55  55   55   Evaluation test results Load resistance (N) 3923    3923   3923    3923    Fatigue life (min) 1424    1592    1569    1580    Shearstability Kinematic viscosity after shear 15.5  15.5  15.5  15.5 Decrease in viscosity (%) 0.7 0.7 0.7 0.7 Friction characteristics  0.08 0.10  0.10  0.10 Example 13 Example 14 Example 15 Example 16 Base oilcomposition (% by mass on the basis of the total amount of base oil) A-1(38)   (38)   (38)   (38)   A-2 (62)   (62)   (62)   (62)   Base oilkinematic viscosity (mm²/s)  40° C. 118.1  118.1  118.1  118.1  100° C.12.7  12.7  12.7  12.7  Sulfur content in base oil 3508    3508   3508    3508    (ppm by mass) Lubricating oil composition (% by mass onthe basis of the total amount of lubricating oil) Base oil BalanceBalance Balance Balance B-1 3.0 3.0 3.0 3.0 C-1 1.5 0.2 0.1 0.1 D-1 2.02.7 3.5 3.5 E-1  0.80  0.80  0.80  0.80 E-2 — — — — E-3  0.09 — — — E-4— — — — F-1 — — —  0.65 G-1 5.0 — — — G-2 — 7.0 — — G-3 — — 7.0 7.0 Dingredient content/C ingredient 1.4 14.9  50   50   content Sulfurcontent in additives 14524     12945     16282     16282     (ppm bymass) Properties of lubricating oil Kinematic viscosity (mm²/s)  40° C.144.3  144.5  144.6  144.9  100° C. 15.6  15.8  15.8  15.7  Viscosityindex 111    111    113    112    Elementary analysis (ppm by mass) P1100    1400    890    1600    S 18032     16453     19790     19790    B 55   150    170    170    Evaluation test results Load resistance (N)3923    3089    3923    3089    Fatigue life (min) 1555    1572   1489    1679    Shear stability Kinematic viscosity after shear 15.5 15.7  15.7  15.6  Decrease in viscosity (%) 0.7 0.7 0.8 0.8 Frictioncharacteristics  0.08  0.09  0.09  0.09

TABLE 3 Example 17 Example 18 Example 19 Example 20 Base oil composition(% by mass on the basis of the total amount of base oil) A-1 (5)  (28)   (38)   (38)   A-2 (80)   (52)   (62)   (62)   A-3 (15)   — — —A-4 — (20)   — — A-6 — — — — Base oil kinematic viscosity (mm²/s)  40°C. 106.6  104.1  118.1  118.1  100° C. 11.7  12.0  12.7  12.7  Sulfurcontent in base oil 4780    2888    3508    3508    (ppm by mass)Lubricating oil composition (% by mass on the basis of the total amountof lubricating oil) Base oil Balance Balance Balance Balance B-1 3.0 3.03.0 3.0 C-1 1.5 1.5 3.4 5.4 D-1 2.3 2.0 2.0 2.0 E-1  0.80  0.80  0.80 0.80 G-1 5.0 5.0 5.0 5.0 D ingredient content/C ingredient 1.6 1.4 0.60.4 content Sulfur content in additives 16521     14524     21544    28744     (ppm by mass) Properties of lubricating oil Kinematicviscosity (mm²/s)  40° C. 129.2  134.2  144.3  144.3  100° C. 14.3 14.9  15.6  15.6  Viscosity index 110    112    111    111    Elementaryanalysis (ppm by mass) P 1100    1100    1100    1100    S 24000    17412     22848     30048     B 55   55   55   55   Evaluation testresults Load resistance (N) 3923    3923    4903    4903    Fatigue life(min) 1456    1581    1501    1322    Shear stability Kinematicviscosity after shear 14.2  14.8  15.5  15.5  Decrease in viscosity (%)0.7 0.7 0.7 0.7 Friction characteristics  0.09  0.09  0.10  0.10 Example21 Example 22 Example 23 Base oil composition (% by mass on the basis ofthe total amount of base oil) A-1 (35)   — — A-2 — — (10)   A-3 (65)   —(30)   A-4 — (100)    — A-6 — — (60)   Base oil kinematic viscosity(mm²/s)  40° C. 54.0  46.7  115.9  100° C. 7.6 7.6 28.1  Sulfur contentin base oil 4260    0   1880    (ppm by mass) Lubricating oilcomposition (% by mass on the basis of the total amount of lubricatingoil) Base oil Balance Balance Balance B-1 3.0 3.0 3.0 C-1 1.5 1.5 1.5D-1 2.0 2.0 2.0 E-1  0.80  0.80  0.80 G-1 5.0 5.0 5.0 D ingredientcontent/C ingredient 1.4 1.4 1.4 content Sulfur content in additives14524     14524     14524     (ppm by mass) Properties of lubricatingoil Kinematic viscosity (mm²/s)  40° C. 78.3  79.3  144.1  100° C. 10.2 10.6  31.7  Viscosity index 112    118    262    Elementary analysis(ppm by mass) P 1100    1100    1100    S 16580     14524     16404    B 55   55   55   Evaluation test results Load resistance (N) 3089   3089    3923    Fatigue life (min) 1115    1217    2019    Shearstability Kinematic viscosity after shear 10.1  10.5  31.6  Decrease inviscosity (%) 0.9 0.5 0.4 Friction characteristics  0.08  0.09  0.09

TABLE 4 Comparative Comparative Comparative Example 1 Example 2 Example3 Base oil composition (% by mass on the basis of the total amount ofbase oil) A-1 (38)   (38)   (38)   A-2 (62)   (62)   (62)   Base oilkinematic viscosity (mm²/s)  40° C. 118.1  118.1  118.1  100° C. 12.7 12.7  12.7  Sulfur content in base oil 3508    3508    3508    (ppm bymass) Lubricating oil composition (% by mass on the basis of the totalamount of lubricating oil) Base oil Balance Balance Balance B-1 — 20.0 — b-1 — — 3.0 b-2 — — — b-3 — — — b-4 — — — C-1 1.5 1.5 1.5 D-1 2.0 2.02.0 E-1  0.80  0.80  0.80 G-1 5.0 5.0 5.0 D ingredient content/C 1.4 1.41.4 ingredient content Sulfur content in additives 14524     14524    14524     (ppm by mass) Properties of lubricating oil Kinematicviscosity (mm²/s)  40° C. 122.9  206.2  143.3  100° C. 13.7  21.0  15.3 Viscosity index 108    121    109    Elementary analysis (ppm by mass) P1100    1100    1100    S 18032     18032     18032     B 55   55   55  Evaluation test results Load resistance (N) 3923    3923    3923   Fatigue life (min) 659    1578    912    Shear stability Kinematicviscosity after 13.6  19.3  15.2  shear Decrease in viscosity (%) 0.18.8 0.5 Friction characteristics  0.09  0.09  0.09 ComparativeComparative Comparative Example 4 Example 5 Example 6 Base oilcomposition (% by mass on the basis of the total amount of base oil) A-1(38)   (38)   (38)   A-2 (62)   (62)   (62)   Base oil kinematicviscosity (mm²/s)  40° C. 118.1  118.1  118.1  100° C. 12.7  12.7  12.7 Sulfur content in base oil 3508    3508    3508    (ppm by mass)Lubricating oil composition (% by mass on the basis of the total amountof lubricating oil) Base oil Balance Balance Balance B-1 — — — b-1 — — —b-2 3.0 — — b-3 — 3.0 — b-4 — — 3.0 C-1 1.5 1.5 1.5 D-1 2.0 2.0 2.0 E-1 0.80  0.80  0.80 G-1 5.0 5.0 5.0 D ingredient content/C 1.4 1.4 1.4ingredient content Sulfur content in additives 14524     14524    14524     (ppm by mass) Properties of lubricating oil Kinematicviscosity (mm²/s)  40° C. 193.2  150.2  169.2  100° C. 19.8  16.0  17.2 Viscosity index 118    111    110    Elementary analysis (ppm by mass) P1100    1100    1100    S 18032     18032     18032     B 55   55   55  Evaluation test results Load resistance (N) 3923    3923    3923   Fatigue life (min) 2021    882    856    Shear stability Kinematicviscosity after 16.6  15.5  15.5  shear Decrease in viscosity (%) 19.6 3.6 11.4  Friction characteristics  0.09  0.09  0.09

TABLE 5 Comparative Comparative Comparative Comparative Example 7Example 8 Example 9 Example 10 Base oil composition (% by mass on thebasis of the total amount of base oil) A-1 (38)   (38)   (38)   (10)  A-2 (62)   (62)   (62)   — A-3 — — — — A-4 — — — — A-5 — — — (90)   A-6— — — — Base oil kinematic viscosity (mm²/s)  40° C. 118.1  118.1 118.1  9.5 100° C. 12.7  12.7  12.7  2.6 Sulfur content in base oil3508    3508    3508    140    (ppm by mass) Lubricating oil composition(% by mass on the basis of the total amount of lubricating oil) Base oilBalance Balance Balance Balance B-1 3.0 3.0 3.0 3.0 C-1 — 1.5 8.0 1.5D-1 2.0 2.0 2.0 2.0 E-1  0.80 —  0.80  0.80 G-1 5.0 5.0 5.0 5.0 G-3 — —— — D ingredient content/C ingredient — 1.4 0.3 1.4 content Sulfurcontent in additives 9182    14524     37910     14524     (ppm by mass)Properties of lubricating oil Kinematic viscosity (mm²/s)  40° C. 144.3 144.3  143.9  32.1  100° C. 15.6  15.6  15.5  5.4 Viscosity index 111   109    110    99   Elementary analysis (ppm by mass) P 1100    1100   1100    1100    S 12690     18032     32252     14664     B 55   55  55   55   Evaluation test results Load resistance (N) 1961    3923   4903    1961    Fatigue life (min) 1256    1578    728    562    Shearstability Kinematic viscosity after shear 15.5  15.5  15.3  5.3 Decreasein viscosity (%) 0.7 0.7 0.9 0.7 Friction characteristics  0.09  0.15 0.09  0.09 Comparative Comparative Comparative Example 11 Example 12Example 13 Base oil composition (% by mass on the basis of the totalamount of base oil) A-1 (38)   (38)   (38)   A-2 (62)   (62)   (62)  A-3 — — — A-4 — — — A-5 — — — A-6 — — — Base oil kinematic viscosity(mm²/s)  40° C. 118.1  118.1  118.1  100° C. 12.7  12.7  12.7  Sulfurcontent in base oil 3508    3508    3508    (ppm by mass) Lubricatingoil composition (% by mass on the basis of the total amount oflubricating oil) Base oil Balance Balance Balance B-1 3.0 3.0 3.0 C-10.1 1.5 1.5 D-1 5.0 — 2.0 E-1  0.80  0.80 2.0 G-1 — 5.0 5.0 G-3 7.0 — —D ingredient content/C ingredient 71   1.4 1.4 content Sulfur content inadditives 23152     5400    14524     (ppm by mass) Properties oflubricating oil Kinematic viscosity (mm²/s)  40° C. 144.6  143.3  144.3 100° C. 15.8  15.4  15.6  Viscosity index 113    110    111   Elementary analysis (ppm by mass) P 890    1100    1100    S 26660    8908    18032     B 170    55   55   Evaluation test results Loadresistance (N) 4903    1961    2452    Fatigue life (min) 908    1301   1344    Shear stability Kinematic viscosity after shear 15.5  15.3 15.5  Decrease in viscosity (%) 2.1 0.7 0.7 Friction characteristics 0.09  0.09  0.07

1. A lubricating oil composition comprising: a lubricating base oil;1.0% by mass or more and 15.0% by mass or less of a dispersantpoly(meth)acrylate compound having a weight average molecular weight of20000 or more and 200000 or less; 0.05% by mass or more and 6.0% by massor less of a thiadiazole compound; 1.5% by mass or more and 4.0% by massor less of a polysulfide compound; and 0.2% by mass or more and 1.5% bymass or less of a friction modifier, based on a total amount of thelubricating oil composition, wherein a mass ratio of the polysulfidecompound content to the thiadiazole compound content (polysulfidecompound/thiadiazole compound) is 0.4 or more and 50 or less, and akinematic viscosity at 100° C. of the lubricating oil composition is 7.0mm²/s or more and 35.0 mm²/s or less.
 2. The lubricating oil compositionaccording to claim 1, wherein the friction modifier comprises at leastone selected from a group consisting of primary or secondary amidefriction modifiers and primary or secondary amine friction modifiers. 3.The lubricating oil composition according to claim 1, wherein thelubricating oil composition is used for gear oils.
 4. The lubricatingoil composition according to claim 1, wherein the lubricating oilcomposition is used for final reduction gear oils.
 5. The lubricatingoil composition according to claim 2, wherein the lubricating oilcomposition is used for gear oils.
 6. The lubricating oil compositionaccording to claim 2, wherein the lubricating oil composition is usedfor final reduction gear oils.